Removes unnecessary setup in ConcurrentInstanceStartupIT
Fixes a bug around an incorrect assumption for remote address on channels

Netty channel's getRemoteAddress() method returns null if the channel is not
 connected. That was not taken into consideration in NetworkSender leading to
 wrong URIs formed and closed channels being reused. This lead to various
 errors. This is now fixed by reverse mapping the channel to the URI and
 also handling channelConnected() events instead of channelOpened.
Tests for the above.